The nervous system
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The Nervous System. Functions of the Nervous System. Sensory input—gathering information To monitor changes occurring inside and outside the body Changes = stimuli Integration To process and interpret sensory input and decide if action is needed. Functions of the Nervous System.

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The Nervous System

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The nervous system

The Nervous System


Functions of the nervous system

Functions of the Nervous System

  • Sensory input—gathering information

    • To monitor changes occurring inside and outside the body

    • Changes = stimuli

  • Integration

    • To process and interpret sensory input and decide if action is needed


Functions of the nervous system1

Functions of the Nervous System

  • Motor output

    • A response to integrated stimuli

    • The response activates muscles or glands


Functions of the nervous system2

Functions of the Nervous System

Figure 7.1


Structural classification of the nervous system

Structural Classification of the Nervous System

  • Central nervous system (CNS)

    • Brain

    • Spinal cord

  • Peripheral nervous system (PNS)

    • Nerves outside the brain and spinal cord

      • Spinal nerves

      • Cranial nerves


Functional classification of the peripheral nervous system

Functional Classification of the Peripheral Nervous System

  • Sensory (afferent) division

    • Nerve fibers that carry information to the central nervous system

  • Motor (efferent) division

    • Nerve fibers that carry impulses away from the central nervous system


Organization of the nervous system

Organization of the Nervous System

Figure 7.2


Functional classification of the peripheral nervous system1

Functional Classification ofthe Peripheral Nervous System

  • Motor (efferent) division (continued)

    • Two subdivisions

      • Somatic nervous system = voluntary

      • Autonomic nervous system = involuntary


Nervous tissue support cells

Nervous Tissue: Support Cells

  • Support cells in the CNS are grouped together as “neuroglia”

  • Function: to support, insulate, and protect neurons


Nervous tissue support cells1

Nervous Tissue: Support Cells

  • Astrocytes

    • Abundant, star-shaped cells

    • Brace neurons

    • Form barrier between capillaries and neurons

    • Control the chemical environment of the brain


Nervous tissue support cells2

Nervous Tissue: Support Cells

Figure 7.3a


Nervous tissue support cells3

Nervous Tissue: Support Cells

  • Microglia

    • Spiderlike phagocytes

    • Dispose of debris


Nervous tissue support cells4

Nervous Tissue: Support Cells

Figure 7.3b


Nervous tissue support cells5

Nervous Tissue: Support Cells

  • Ependymal cells

    • Line cavities of the brain and spinal cord

    • Circulate cerebrospinal fluid


Nervous tissue support cells6

Nervous Tissue: Support Cells

Figure 7.3c


Nervous tissue support cells7

Nervous Tissue: Support Cells

  • Oligodendrocytes

    • Wrap around nerve fibers in the central nervous system

    • Produce myelin sheaths


Nervous tissue support cells8

Nervous Tissue: Support Cells

Figure 7.3d


Nervous tissue support cells9

Nervous Tissue: Support Cells

  • Satellite cells

    • Protect neuron cell bodies

  • Schwann cells

    • Form myelin sheath in the peripheral nervous system


Nervous tissue support cells10

Nervous Tissue: Support Cells

Figure 7.3e


Nervous tissue neurons

Nervous Tissue: Neurons

  • Neurons = nerve cells

    • Cells specialized to transmit messages

    • Major regions of neurons

      • Cell body—nucleus and metabolic center of the cell

      • Processes—fibers that extend from the cell body


Nervous tissue neurons1

Nervous Tissue: Neurons

  • Cell body

    • Nissl substance

      • Specialized rough endoplasmic reticulum

    • Neurofibrils

      • Intermediate cytoskeleton

      • Maintains cell shape


Nervous tissue neurons2

Nervous Tissue: Neurons

Figure 7.4


Nervous tissue neurons3

Nervous Tissue: Neurons

  • Cell body

    • Nucleus

    • Large nucleolus

  • Processes outside the cell body

    • Dendrites—conduct impulses toward the cell body

    • Axons—conduct impulses away from the cell body


Nervous tissue neurons4

Nervous Tissue: Neurons

Figure 7.4


Nervous tissue neurons5

Nervous Tissue: Neurons

  • Axons end in axonal terminals

  • Axonal terminals contain vesicles with neurotransmitters

  • Axonal terminals are separated from the next neuron by a gap

    • Synaptic cleft—gap between adjacent neurons

    • Synapse—junction between nerves


Nervous tissue neurons6

Nervous Tissue: Neurons

  • Myelin sheath—whitish, fatty material covering axons

  • Schwann cells—produce myelin sheaths in jelly roll–like fashion

  • Nodes of Ranvier—gaps in myelin sheath along the axon


Nervous tissue neurons7

Nervous Tissue: Neurons

Figure 7.5


Neuron cell body location

Neuron Cell Body Location

  • Most neuron cell bodies are found in the central nervous system

    • Gray matter—cell bodies and unmyelinated fibers

    • Nuclei—clusters of cell bodies within the white matter of the central nervous system

  • Ganglia—collections of cell bodies outside the central nervous system


Functional classification of neurons

Functional Classification of Neurons

  • Sensory (afferent) neurons

    • Carry impulses from the sensory receptors to the CNS

      • Cutaneous sense organs

      • Proprioceptors—detect stretch or tension

  • Motor (efferent) neurons

    • Carry impulses from the central nervous system to viscera, muscles, or glands


Functional classification of neurons1

Functional Classification of Neurons

Figure 7.7


Functional classification of neurons2

Functional Classification of Neurons

  • Interneurons (association neurons)

    • Found in neural pathways in the central nervous system

    • Connect sensory and motor neurons


Neuron classification

Neuron Classification

Figure 7.6


Structural classification of neurons

Structural Classification of Neurons

  • Multipolar neurons—many extensions from the cell body

Figure 7.8a


Structural classification of neurons1

Structural Classification of Neurons

  • Bipolar neurons—one axon and one dendrite

Figure 7.8b


Structural classification of neurons2

Structural Classification of Neurons

  • Unipolar neurons—have a short single process leaving the cell body

Figure 7.8c


Functional properties of neurons

Functional Properties of Neurons

  • Irritability

    • Ability to respond to stimuli

  • Conductivity

    • Ability to transmit an impulse


Nerve impulses

Nerve Impulses

  • Resting neuron

    • The plasma membrane at rest is polarized

    • Fewer positive ions are inside the cell than outside the cell

  • Depolarization

    • A stimulus depolarizes the neuron’s membrane

    • A depolarized membrane allows sodium (Na+) to flow inside the membrane

  • The exchange of ions initiates an action potential in the neuron


Nerve impulses1

Nerve Impulses

Figure 7.9a–b


Nerve impulses2

Nerve Impulses

  • Action potential

    • If the action potential (nerve impulse) starts, it is propagated over the entire axon

    • Impulses travel faster when fibers have a myelin sheath


Nerve impulses3

Nerve Impulses

Figure 7.9c–d


Nerve impulses4

Nerve Impulses

  • Repolarization

    • Potassium ions rush out of the neuron after sodium ions rush in, which repolarizes the membrane

    • The sodium-potassium pump, using ATP, restores the original configuration


Nerve impulses5

Nerve Impulses

Figure 7.9e–f


Transmission of a signal at synapses

Transmission of a Signal at Synapses

  • Impulses are able to cross the synapse to another nerve

    • Neurotransmitter is released from a nerve’s axon terminal

    • The dendrite of the next neuron has receptors that are stimulated by the neurotransmitter

    • An action potential is started in the dendrite


Transmission of a signal at synapses1

Axonterminal

Actionpotentialarrives

Axon oftransmittingneuron

Vesicles

Synapticcleft

Receivingneuron

Synapse

Transmitting neuron

Neurotrans-mitter bindsto receptoron receivingneuron’smembrane

Vesiclefuses withplasmamembrane

Neurotrans-mitter is re-leased intosynaptic cleft

Neurotransmittermolecules

Synaptic cleft

Ion channels

Receiving neuron

Neurotransmitterbroken downand released

Neurotransmitter

Receptor

Na+

Na+

Ion channel opens

Ion channel closes

Transmission of a Signal at Synapses

Figure 7.10


Transmission of a signal at synapses2

Axonterminal

Actionpotentialarrives

Axon oftransmittingneuron

Vesicles

Synapticcleft

Receivingneuron

Synapse

Transmission of a Signal at Synapses

Figure 7.10, step 1


Transmission of a signal at synapses3

Axonterminal

Axon oftransmittingneuron

Actionpotentialarrives

Vesicles

Synapticcleft

Receivingneuron

Synapse

Transmitting neuron

Vesiclefuses withplasmamembrane

Synaptic cleft

Ion channels

Receiving neuron

Transmission of a Signal at Synapses

Figure 7.10, step 2


Transmission of a signal at synapses4

Axonterminal

Axon oftransmittingneuron

Actionpotentialarrives

Vesicles

Synapticcleft

Receivingneuron

Synapse

Transmitting neuron

Vesiclefuses withplasmamembrane

Neurotrans-mitter is re-leased intosynaptic cleft

Neurotransmittermolecules

Synaptic cleft

Ion channels

Receiving neuron

Transmission of a Signal at Synapses

Figure 7.10, step 3


Transmission of a signal at synapses5

Axonterminal

Axon oftransmittingneuron

Actionpotentialarrives

Vesicles

Synapticcleft

Receivingneuron

Synapse

Transmitting neuron

Neurotrans-mitter bindsto receptoron receivingneuron’smembrane

Vesiclefuses withplasmamembrane

Neurotrans-mitter is re-leased intosynaptic cleft

Neurotransmittermolecules

Synaptic cleft

Ion channels

Receiving neuron

Transmission of a Signal at Synapses

Figure 7.10, step 4


Transmission of a signal at synapses6

Axonterminal

Axon oftransmittingneuron

Actionpotentialarrives

Vesicles

Synapticcleft

Receivingneuron

Synapse

Transmitting neuron

Neurotrans-mitter bindsto receptoron receivingneuron’smembrane

Vesiclefuses withplasmamembrane

Neurotrans-mitter is re-leased intosynaptic cleft

Neurotransmittermolecules

Synaptic cleft

Ion channels

Receiving neuron

Neurotransmitter

Receptor

Na+

Ion channel opens

Transmission of a Signal at Synapses

Figure 7.10, step 5


Transmission of a signal at synapses7

Axonterminal

Axon oftransmittingneuron

Actionpotentialarrives

Vesicles

Synapticcleft

Receivingneuron

Synapse

Transmitting neuron

Neurotrans-mitter bindsto receptoron receivingneuron’smembrane

Vesiclefuses withplasmamembrane

Neurotrans-mitter is re-leased intosynaptic cleft

Neurotransmittermolecules

Synaptic cleft

Ion channels

Receiving neuron

Neurotransmitterbroken downand released

Neurotransmitter

Receptor

Na+

Na+

Ion channel opens

Ion channel closes

Transmission of a Signal at Synapses

Figure 7.10, step 6


Transmission of a signal at synapses8

Axonterminal

Actionpotentialarrives

Axon oftransmittingneuron

Vesicles

Synapticcleft

Receivingneuron

Synapse

Transmitting neuron

Neurotrans-mitter bindsto receptoron receivingneuron’smembrane

Vesiclefuses withplasmamembrane

Neurotrans-mitter is re-leased intosynaptic cleft

Neurotransmittermolecules

Synaptic cleft

Ion channels

Receiving neuron

Neurotransmitterbroken downand released

Neurotransmitter

Receptor

Na+

Na+

Ion channel opens

Ion channel closes

Transmission of a Signal at Synapses

Figure 7.10, step 7


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